Mass-body drive for a rotary tightening device

ABSTRACT

A rotary tightening device for a safety belt has a belt retractor including a housing and a belt take-up shaft rotatably supported in the housing. The belt-take-up shaft has one end of the safety belt connected thereto. Upon triggering of the rotary tightening device, the belt take-up shaft is rotated in a belt take-up direction of the safety belt. A drive wheel is connected to the shaft. The housing has a channel extending in a plane parallel to a radial plane of the drive wheel and extending at least partially about a circumference of the drive wheel. Mass bodies are positioned loosely adjacent to one another in the channel. The mass bodies, when accelerated, act on the drive wheel for driving it. The drive wheel has at the circumference a gearing in which the mass bodies are received for driving the drive wheel. A spacing of the gearing is substantially identical to a spacing between the mass bodies.

BACKGROUND OF THE INVENTION

The invention relates to a rotary tightening device for a safety belt,particularly in motor vehicles, having a belt retractor, whose belttake-up shaft upon triggering of the rotary tightening device coupledthereto is rotated in the take-up direction of the safety belt, therebeing associated with the belt take-up shaft, as a drive, a drivingwheel in whose plane the housing of the belt retractor forms a channel,which embraces the driving wheel over at least part of its periphery,for the through passage of mass bodies acting as driving means upon thedriving wheel and lying loosely adjacent to one another in the channel.

The basic construction of a rotary tightening device having the featuresmentioned above is described in DE 29 31 164 A1; in the known rotarytightening device, the belt take-up shaft is provided with a drivingwheel, the housing in the plane of the driving wheel having a channelwhich embraces the driving wheel over part of its periphery; in saidchannel, mass bodies are driven under the action of a pyrotechnic driveout of a tube disposed tangentially to the driving wheel or the channeland as a result of their friction-locking connection to the drivingwheel, which for said purpose is provided with a circumferentialcontoured groove, set said driving wheel in rotation as they run throughthe channel. According to an embodiment, the mass bodies may take theform of balls made of a suitably hard plastics material. An outletopening for the mass bodies may be provided at the end of the channel,the mass bodies exiting from the channel through said outlet opening andpassing into a suitably provided receiving container.

A drawback of said known rotary tightening device is that the drive iseffected through friction locking; consequently, on the one hand,considerable energy is lost and, on the other hand, it is difficult totune the contoured groove and the mass bodies to one another in such away as to produce a defined friction lock and prevent the mass bodiesfrom becoming wedged or sliding through without power transmission. Afurther drawback associated with the known rotary tightening device isthat-when the hard mass bodies encounter the driving wheel, because thechannel for sealing reasons has only slight clearance, a mutual blockingbetween the periphery of the driving wheel and the mass bodies may arisein the channel, thereby impairing the efficiency of the drive in theevent of triggering.

The object of the invention is therefore to improve a rotary tighteningdevice having the features described initially in such a way that thetransmission of the drive power, which is imparted to the mass bodies,to the tightening rotation of the belt take-up roller is improved.

SUMMARY OF THE INVENTION

A rotary tightening device for a safety belt according to the presentinvention is primarily characterized by:

a belt retractor comprising a housing and a belt take-up shaft rotatablysupported in the housing, the belt-take-up shaft having one end of thesafety belt connected thereto and, upon triggering of the rotarytightening device, being rotated in a belt take-up direction of thesafety belt;

a drive wheel connected to the shaft;

the housing having a channel extending in a plane parallel to a radialplane of the drive wheel and extending at least partially about acircumference of the drive wheel;

mass bodies positioned loosely adjacent to one another in the channel;

the mass bodies, when accelerated, acting on the drive wheel for drivingthe drive wheel;

the drive wheel having at the circumference a gearing in which the massbodies are received for driving the drive wheel, wherein a spacing ofthe gearing is substantially identical to a spacing between the massbodies.

The gearing is designed such that the mass bodies, when received in thegearing, contact one another.

The gearing is preferably comprised of recesses projecting radiallyinwardly from the circumference of the drive wheel.

The gearing is advantageously comprised of cup-shaped recesses at thecircumference of the drive wheel, the cup-shaped recesses having a shapematching a shape of the mass balls.

The cup-shaped recesses are expediently positioned along the entirecircumference and are contiguous.

The cup-shaped recesses are preferably positioned along the entirecircumference and slightly overlap one another.

The mass bodies are balls and the cup-shaped recesses are sphericalhalf-shells.

The radius of the cup-shaped recesses originates at a circle defined bythe theoretical points of contact of successive ones of the balls andextends to a center of the circle.

Preferably, the cup-shaped recesses widen radially outwardly in a funnelshape.

The cup-shaped recesses have transitions into neighboring ones of thecup-shaped recesses. The transitions between the cup-shaped recesses areproduced by rolling a milling cutter for milling the cup-shaped recessesalong a circular path, having a radius identical to the radius of thecup-shaped recesses.

The outside diameter of the drive wheel is greater than the thrustdiameter by a distance ≦a diameter of the balls.

The rotary tightening device may further comprise a casing for securingthe balls therein.

The casing comprises a plastic tube in which the balls are positioned.The casing may be an extrusion coating applied to the balls.

Expediently, the rotary tightening device may further comprise acollecting chamber for the drive balls, wherein the balls are guidedtangentially along the circumference of the drive wheel for driving thedrive wheel and thereafter are collected in the collecting chamber.

The angular distance of interaction between the balls and the gearing isup to 45°.

The drive wheel has a peripheral groove cutting through the cup-shapedrecesses and the housing has sword-shaped guides for the mass balls, thesword-shaped guides extending into the groove.

The drive wheel has an inlet region for the balls and an outlet regionfor the balls, wherein one of the sword-shaped guides is positioned atthe inlet region and another of the sword-shaped guides is positioned atthe outlet region.

The drive wheel is divided into two halves in the area of the groove andone of the halves is connected to the belt take-up shaft.

The half connected to the belt take-up shaft and the belt take-up shaftare a unitary part.

A first one of the halves consists of a different material than a secondone of the halves.

The rotary tightening device may further comprise a collecting devicefor collecting the mass bodies when exiting from the drive wheel, thecollecting device comprising an open, flexible collecting tube and acollecting chamber. The collecting tube opens into the collectingchamber.

The rotary tightening device may instead comprise a collecting devicefor collecting the mass bodies when exiting from the drive wheel in theform of a folded receptacle positioned within a contour of the rotarytightening device, wherein the receptacle unfolds upon triggering of therotary tightening device.

In another embodiment of the present invention, the rotary tighteningdevice for a safety belt is primarily characterized by:

a belt retractor comprising a housing and a belt take-up shaft rotatablysupported in the housing, the belt-take-up shaft having one end of thesafety belt connected thereto and, upon triggering of the rotarytightening device, being rotated in a belt take-up direction of thesafety belt;

a drive wheel connected to the shaft;

the housing having a channel extending in a plane parallel to a radialplane of the drive wheel and extending at least partially about acircumference of the drive wheel;

mass bodies positioned loosely adjacent to one another in the channel;

the mass bodies, when accelerated, acting on the drive wheel for drivingthe drive wheel;

the channel being a tube connected to the belt retractor;

the tube bent so as to provide a helical course for the mass bodiesextending from the outside inwardly toward the shaft and having adecreasing radius along the helical course in a direction toward theshaft.

The rotary tightening device further comprises a cap made of resistantmaterial for mounting the tube to the retractor, wherein the cap has areceiving element for positive-lockingly securing the tube thereat.

The tube preferably has a bead and the cap has a matching throat forreceiving the bead.

The tube has a free end with a U-shaped suspending member and the caphas a matching receiver for receiving the U-shaped suspending member.

The tube is mounted in a load-transmitting manner on the housing of thebelt retractor.

The rotary tightening device may further comprise a cap, consisting ofplastic material, connected to the housing of the belt retractor,wherein the tube is embedded in the cap.

The tube is preferably seamless.

The tube may be comprised of tube halves seam-welded to one another.

The rotary tightening device may comprise a gas generator mounted withinthe tube, the gas generator accelerating sequentially the mass bodies,when activated, in a longitudinal direction of the gas generator, thetube having securing elements for positive-lockingly securing the gasgenerator.

The rotary tightening device may also comprise a drive piston consistingof elastic material and positioned between the gas generator and themass bodies.

The drive piston is secured in the tube at a distance to the gasgenerator for defining an initial volume, the tube having means forpositive-lockingly securing the drive piston.

The rotary tightening device may comprise a spring positioned betweenthe drive piston and the gas generator for supporting the piston.

The drive piston has a periphery with an elastic, outwardly directedspreading means and the tube has a groove positioned in a runningdirection of the mass bodies at a free end of the tube, wherein thespreading means engages the groove after all mass bodies have beenreleased from the tube.

The tube comprises bores at an end thereof from which the mass bodiesare discharged, the bores allowing escape of the propellant of the gasgenerator.

The rotary tightening device includes a pressure relief devicepositioned in an area between the drive piston and the gas generatorwhere the initial volume is defined, the pressure relief devicecomprising a breaking point opening a window for pressure relief when apressure threshold is surpassed.

The rotary tightening device may also include a collecting device forcollecting the mass bodies when exiting from the drive wheel, thecollecting device comprising an open, flexible collecting tube and acollecting chamber, the collecting tube opening into the collectingchamber.

The rotary tightening device may include a collecting device forcollecting the mass bodies when exiting from the drive wheel in the formof a folded receptacle positioned within a contour of the rotarytightening device, wherein the receptacle unfolds upon triggering of therotary tightening device.

In principle, the teaching of the invention is such that the drivingwheel is provided at its outer periphery with a gearing for receivingthe mass bodies, the pitch substantially corresponding to the spacing ofthe mass bodies. The invention offers the advantage that by means of thegearing formed on the periphery of the driving wheel a form-fitreceiving of the mass bodies is realized, as a result of which the powertransmission between the mass bodies and the driving wheel for thebelt-take-up shaft is markedly improved.

According to an embodiment of the invention, it is provided that thegearing of the driving wheel for receiving the mass bodies isconstructed in such a way that the mass bodies, upon engagement so as tooverlap the gearing, remain permanently in contact with other; by saidmeans, the efficiency of power transmission is advantageously furtherimproved.

According to an embodiment of the invention, the gearing of the drivingwheel is formed by recesses which extend beyond the outer periphery ofthe driving wheel, the gearing on the periphery of the driving wheelpreferably taking the form of cup-shaped recesses which are adapted tothe shape-of the mass bodies. The effect thereby achieved is an axial,i.e. lateral, guidance of the mass bodies in the driving wheel as wellas synchronous running of the mass bodies in the driving wheel. Asimultaneous effect achieved by the receiving of the mass bodies in thecup-shaped recesses is optimum threading of the first mass body toencounter the driving wheel or pass into its periphery after triggeringof the drive.

Said cup-shaped construction of the flanks of the corresponding gearingmoreover provides a large contact surface for the individual massbodies, thereby substantially reducing deformation of the two structuralparts; extreme deformation of the mass bodies would lead to wedging inthe driving wheel and hence ultimately to blocking of the driving wheel.

According to an embodiment of the invention, it is provided that thecup-shaped recesses continuously disposed over the periphery of thedriving wheel are contiguous. This offers the advantage of reliablymaintaining the thrust connection between the individual adjacent massbodies as they run through the driving wheel and preventing separationof the mass bodies and hence interruption of the drive flow between themass bodies as well as power losses for separation of the individualmass bodies. According to an embodiment of the invention, said advantageis enhanced in that the cup-shaped recesses continuously disposed overthe periphery of the driving wheel overlap one another by a smallamount. In an embodiment of the invention, it is provided that the massbodies take the form of mass balls and the cup-shaped recesses take theform of spherical half-shells in the driving wheel. To said end, in anembodiment the invention further provides that the radius of thecup-shaped recesses lies on the thrust diameter defined by thetheoretical points of contact of the successive mass bodies.

To guarantee efficient threading of the mass balls into the drivingwheel, according to an embodiment of the invention a funnel-likewidening of the cup-shaped recess is provided, and according to anembodiment of the invention the cup-shaped recesses in each case have atransition between them.

An optimum shape of the transition between the cup-shaped recesses isproduced when the transition lies on a circular path between the centresof the cup-shaped recesses, said circular path having a diametercorresponding to the diameter of the cup-shaped recess. To achieve agreater contact ratio between the mass balls and the cup-shapedrecesses, the circular path may be disposed on a larger diameter thanthe thrust diameter.

To achieve threading of the individual mass balls, according to anembodiment of the invention it may be provided that the outside diameterof the driving wheel is greater by up to one mass ball diameter than thethrust diameter of the mass balls.

For greater ease of assembly and precise positioning of the mass ballsin the channel, the moulded balls may be "magazined" in a continuouscasing and said casing may be deformable in order to improve the inwarddirecting process between the mass balls and the gearing of the drivingwheel. By virtue of the continuous casing, a continuous string of massballs is formed and, by simply cutting said string, a required lengthhaving the desired number of bodies may be obtained. The mass balls thuspositioned are held by the casing by means of friction in the desiredposition in the channel, the casing simultaneously also effecting animproved sealing-off of the mass balls from the wall of the channel.According to embodiments of the invention, the casing may comprise aplastics tube, in which the moulded balls are received and positioned,or the casing may alternatively be formed by extrusion-coating the massballs with a suitable material.

According to an embodiment of the invention, with regard to the courseof the channel it is provided that the mass balls are conveyed only on atangential course past the outer periphery of the driving wheel and,after engagement with the gearing of the driving wheel, pass into acollecting container, with the result that the mass balls do notco-rotate with the driving wheel over a greater angular range, therebyavoiding the friction which would otherwise arise. According to anembodiment of the invention, it is provided that the area of contactbetween the mass balls and the gearing of the driving wheel extends onlyover an angle at circumference of up to 45°.

In order to guarantee efficient guidance of the mass balls as they runthrough, according to an embodiment of the invention it is provided thatthe driving wheel over its periphery has a groove, which cuts thecup-shaped recesses, for receiving a housing-fixed, sword-shaped guidefor the mass balls. Here, it may be sufficient to provide a respectivesword-shaped guide on the inlet side of the driving wheel and also onthe outlet side of the driving wheel for the mass balls. In so far asthe arrangement of a groove is mentioned in DE 29 31 164 Al, saidgroove, described as a contoured groove, has a different functioncompared to the groove in the context of the present invention.

According to an embodiment of the invention, it may be provided that thedriving wheel in the region of the groove is divided into two parts andone half of the driving wheel is connected to the belt take-up shaft;this enables, in particular, greater ease of assembly of the individualparts of the tightening device. According to an embodiment of theinvention, it may then be advantageous for the half of the drivingwheel, which is associated with the belt take-up shaft, to be integrallyconstructed with the belt take-up shaft.

Such a construction of the rotary tightening device moreover allows thetwo halves of the driving wheel, from a production engineeringstandpoint, to be manufactured from different materials.

A further aspect of the invention is geared towards the arrangement ofthe channel in a rotary tightening device and, in said regard, in aspecial embodiment of the invention it is provided that the channel isformed in a tube disposed in the belt retractor housing and following ahelical course, which extends from the outside in towards the belttake-up shaft and has a decreasing radius in relation to the belttake-up shaft.

With regard to the mounting of the tube on the belt retractor housing,according to an embodiment of the invention a cap made of a resistantmaterial is provided, which is provided with a form-fit shaping forfixing the tube on the cap; said form-fit shaping may, according to anembodiment of the invention, be such that the tube is provided with abead and the cap is provided with a matching throat for receiving thebead of the tube; alternatively, the tube may be suspended by a U-shapedbend disposed at its free end in a correspondingly shaped receiver inthe cap. The resistant cap is preferably made of metal, e.g. is analuminium die casting.

It may likewise be provided that the tube is connected in aload-transmitting manner to the housing of the belt retractor by meansof suitable and separate holding devices.

It may however be sufficient to embed and hence fix the tube in a capmade of plastics material, which is connected to the belt retractor.

According to embodiments of the invention, the tube itself may be aseamless structural part or comprise two halves which are seam-welded toone another.

According to an embodiment of the invention, it may be provided that thegas generator is disposed with the mass balls in a line in the axis ofthe tube, in which case the gas generator is locked and fixed inposition through suitable shaping in the tube.

To transmit the drive power from the gas generator to the mass balls, adrive piston made of elastic material is disposed, which drive pistonfor defining an initial volume may be fixed with clearance relative tothe gas generator by means of shapings in the tube. Moreover, it may beprovided that, to prevent noise, the drive piston is fixed by means of asupporting spring against the gas generator and is acted upon by thespring.

To prevent the drive piston from coming into contact with the gearing ofthe driving wheel after the mass balls have run through the tube, thetransmission piston may be provided with elastic, outward-actingspreading means, the tube at the relevant end having a groove, intowhich the spreading means engage and hence fix the drive piston in thetube before the drive piston comes into contact with the driving wheel.

Alternatively, overflow bores which effect stopping of the drive pistonmay be provided in the tube at the end of the appropriate piston travel.

If, in the realization of the invention, a collecting container hasalready been provided for the mass balls after they have run through andexited from the channel or the tube, according to an embodiment of theinvention there is disposed at the end of the tube an open collectingtube made of a flexible material, which opens into the collectingcontainer and suitably brakes the mass balls as they exit from thechannel. To keep the overall size of the rotary tightening device to aminimum, according to the invention the use is further provided of acollapsible collecting device which, when not in use, is situated insidethe contour of the tightening device and only upon activation by themass bodies is unfolded beyond the contour of the belt tighteningdevice.

BRIEF DESCRIPTION OF DRAWINGS

There follows a description of an embodiment of the invention which isillustrated in the drawings. The drawings show:

FIG. 1 a three-dimensional view of a belt take-up shaft with atightening device drive,

FIG. 2 a detail view of the driving wheel,

FIG. 3 a diagrammatic view of the association between driving wheel andmass balls,

FIG. 4 a detail view of a driving wheel with cup-shaped recesses,

FIG. 5 the subject of FIG. 1 in another constructional form,

FIG. 6 the subject of FIG. 1 in a further constructional form,

FIG. 7 another embodiment of a rotary tightening device acting upon thebelt take-up shaft of a belt retractor, in a diagrammatic plan view ofthe front of the belt retractor housing,

FIG. 8 another constructional form of the rotary tightening device shownin FIG. 7,

FIG. 9 an enlarged view of the connection of the gas generator to thechannel in rotary tightening devices according to FIG. 7 or 8.

DESCRIPTION OF PREFERRED EMBODIMENTS

In a manner not shown in greater detail, a belt take-up shaft 10 isrotatably mounted in a belt retractor housing generally of a U-shapedand load-absorbing design. In order to set the belt take-up shaft into arotation which tightens the webbing wound on the shaft, apyrotechnically actuated drive is provided, which comprises a drivingwheel made up of the two driving wheel halves 11, 12, the driving wheelhalf 11 in the illustrated embodiment being firmly connected to the belttake-up shaft 10; as FIG. 1 reveals, the second driving wheel half 12during assembly of the rotary tightening device is then placed againstthe first driving wheel half 11 and connected thereto by means of agearing 31. Disposed between the two driving wheel halves 11, 12 is asword box 13 which is to be associated with the housing of the beltretractor, carries sword-shaped guides 14, 15 extending between the twodriving wheel halves 11, 12 and whose inner periphery 30 encloses theouter periphery of the driving wheel 11, 12.

Disposed in the plane of the sword box 13 and the driving wheel 11, 12is a curved tube 16, in the inner channel of which are stored the massballs 18 used to accelerate the driving wheel 11, 12. Disposed at oneend of the tube 16 is a gas generator receiver 17 containing a gasgenerator (not shown in detail), from which in the event of triggering agas is released and drives the mass balls 18 out of the tube 16; to saidend, a drive piston 19 provided with a seal is disposed in the tube 16and associated with the gas generator receiver 17, while a tube closure20 is situated at the opposite end. Seated externally on the tube 16 isa cap 22, which is connected to the associated U-limb (not shown) of thebelt retractor housing and in the process also carries and supports thetube 16 and the sword box 13.

The basic construction of the driving-wheel 11, 12 is revealed in detailin FIG. 2; continuously disposed on the outer periphery of the drivingwheel are cup-shaped recesses 23 which are adapted to the shape of themass balls 18, i.e. have a radius 32 which is identical to, or slightlygreater than, that of the mass balls 18.

As is shown in detail in FIG. 4, the individual cup-shaped recesses 23lie on the thrust diameter 26 defined by the theoretical points ofcontact 33 of the successive mass balls 18. Said thrust diameter 26 maybe slightly smaller than theoretically calculated in order to take intoaccount the deformation/flattening of the mass balls 18 under the highsurface pressure. The individual cup-shaped recesses 23 aremanufactured, for example, by radial infeed 38 of a suitable shapingbody, for example a milling cutter 34, the transition 23a between theindividual cup-shaped recesses 23 being produced by rolling the millingcutter 34 along a circular path 35 between the points of contact 33,said circular path likewise having a radius 36 corresponding to theradius 32 of the cup-shaped recesses; the illustrated driving wheel 11,12 has a pitch 37 corresponding to the eleven cup-shaped recesses 23.

As is evident from a combined viewing of FIGS. 1 and 2, the drivingwheel comprising the two driving wheel halves 11, 12 has a groove 24,which extends continuously over its periphery and into which the twosword-shaped guides 14, 15 carried by the sword box 13 engage. Asword-shaped guide 15 is first provided in the open inlet region 28 ofthe mass balls 18 into the driving wheel provided in the tube 16 andfacilitates threading of the mass balls 18 into the cup-shaped recesses23, while a sword-shaped guide 14 acting as a stripper is additionallyformed in the outlet region 29, in which the mass balls 18 are to beconveyed back out of the cup-shaped recesses 23 of the driving wheel.

As is evident from FIG. 3, the groove diameter 25 lies radially at thedeepest-point of the cup-shaped recesses 23; in the illustratedembodiment, moreover, the outside diameter 27 of the driving wheel 11,12 is slightly greater than the thrust diameter 26 defined by thetheoretical points of contact 33 of the successive mass balls 18.

Upon triggering of the gas generator seated in the gas generatorreceiver 17, the released gases drive the mass balls 18 stored in thetube 16 out of the tube, the mass balls 18 in the open inlet region 28being driven in a form-fit manner into the cup-shaped recesses 23 of thedriving wheel 11, 12, with assisted guidance by the sword-shaped guide15 of the sword box 13; the mass balls driven successively in mutualcontact radially into the driving wheel 11, 12 set the driving wheel 11,12 in rotation so that the belt take-up shaft 10 executes the desiredrotational movement in tightening direction. After the mass balls 18have run past radially, the mass balls 18 are removed and collected bymeans of the sword-shaped guide 14 acting as a stripper. During saidprocess, the sword-shaped guides 14, 15 prevent an escape of theindividual mass balls 18 from the desired tangential path into thedriving wheel 11, 12 which guarantees optimum power transmission. Inorder also to guarantee operation of the belt retractor after thetightening process, a clean separation of the mass balls 18 from thedriving wheel 11, 12 is provided by the sword-shaped guide 14 acting asa stripper.

FIGS. 5 and 6 each show different constructions with regard to themounting of the tube 16 on the cap 22, the cap for absorbing stressbeing made of metal, preferably being an aluminium die casting, andbeing firmly connected to the belt retractor housing (not shown). In theembodiment shown in FIG. 5, the tube 16 at its opposite end to the gasgenerator receiver 17 has a bead 41, associated with which is acorrespondingly shaped throat 42 on the cap 22 so that, upon assembly ofthe structural parts, the tube 16 is fixed on the cap 22. An alternativefastening is shown in FIG. 6, in which the corresponding end of the tube16 carries a U-shaped bend 43, the free end of which is T-shaped; thecap 22 has a matching receiver 44 of a corresponding shape, at which thetube 16 may therefore be fixed.

FIG. 6 reveals further details, over and above the view of FIG. 1,whereby operation of the rotary tightening device is guaranteed.

Thus, to prevent clattering noises, the drive piston 19 or alternativelythe first mass body 18 is supported by means of a supporting spring 45against the gas generator seated in the gas generator receiver 17. Thedrive piston 19 further has on its outer periphery elastic,outward-acting spreading means 46 and in the tube 16 there is,associated with said spreading means 46 at the end of the distance to betravelled by the drive piston 19 in the tube 16, a groove 47 in whichthe spreading means 46 of the drive piston 19 catch, thereby preventingthe drive piston 19 from entering the recesses 23 of the driving wheel11, 12. Alternatively or additionally, overflow bores 48 may be formedin the tube 16 at the relevant end of the operating travel of the drivepiston 19, the drive piston 19 upon reaching said overflow bores beingno longer pressure-loaded owing the outward flow of the propelling gasand hence being brought to a standstill.

In the region of the transition between the gas generator disposed inthe gas generator receiver 17 and the drive piston 19, the gas generatorreceiver 17 may have a desired breaking point 49, which acts as apressure relief device in order, e.g. in the event of blocking of thedrive, to guarantee safe discharge of the excess pressure generated bythe gas generator in the system because, in the event of such excesspressure, the desired breaking point tears open and releases a windowenabling the gas to flow off.

FIGS. 7 and 8 illustrate embodiments of the invention, in which thedriving wheel for a rotary tightening device takes the form of a simplepinion provided with an external gearing and is connected to the belttake-up shaft.

In the embodiment shown in FIG. 7, the belt take-up shaft 10 is mountedin a housing 51 of a belt retractor 50 and engages with an axialextension through the associated side limb 53 of the housing 51; mountedon the extension in a keyed manner is a pinion 54 as a driving wheelwith an external gearing 55.

The side limb 53 of the housing 51, or a separate structural partmounted thereon, forms within it a channel 56 which at one end has apreferably pyrotechnic unit 57. The channel 56 is formed in the housing51 or its side limb 53 or the associated structural part with a helicalcourse directed from the outside in towards the belt take-up shaft 10,and indeed with a decreasing radius in relation to the belt take-upshaft 10, until the channel 56 tangentially meets the pinion 54 or itsexternal gearing 55 and at said point forms, for the mass bodies 18which are situated in the channel 56 and are to be driven in the eventof triggering by the pyrotechnic drive unit, an area of engagement 58with the external gearing 55 of the pinion 54.

The channel 56 encloses part of the periphery of the pinion 54 and opensinto an outlet opening 60 in an offset plane, through which the massbodies 18 driven in the channel 56 leave the channel 56, for whichpurpose the belt retractor 50 is provided with a collecting container(not shown in detail) of the type basically described in DE 29 31 164A1.

The mass bodies 18 are surrounded by a continuous casing 61 so that acontinuous string of mass bodies is formed. The casing 61 may comprise aplastics tube, in which the mass bodies 18 are introduced andpositioned, or alternatively a continiuous and coherent extrusioncoating of the individual mass bodies. By cutting the continuous stringthe required length may be adjusted, said string because of the flexiblenature of its material on the one hand effecting a sealing-off of themass bodies 18 in the channel 56 but at the same time also improving theinward directing process between the mass bodies 18 and the gearing 55of the pinion 54.

The alternative embodiment of a rotary tightening device shown in detailin FIG. 8 is substantially identical in construction to the embodimentaccording to FIG. 7 described above and, to said extent, identical partsare provided with the same reference numerals. In the embodiment shownin FIG. 8, the channel 56 extends in a separate and, in accordance withthe embodiment of FIG. 7, curved tube 62, which is seamless or comprisestwo seam-welded halves; the tube 62 is inserted in a cap 63, made ofplastics material and connected to the housing 51 of the belt retractor50, and connected with an interference fit to the housing 51 by means ofclamps 64.

Integrated into the tube 62 at its inlet end is a gas generator 65,which is fixed by means of a necking 66 in the tube. Disposed betweenthe outlet of the gas generator 65 and the first mass body 18 is atransmission piston 67 as a drive piston made of an elastic material,said transmission piston 67 in order to form an initial volume 68 beingdisposed with clearance relative to the gas generator 65 and, on theother hand, being fixed by a shaping 69 in the form of neckings in themanner shown in detail in FIG. 9.

The area of action between the mass balls 18 and the external gearing 55of the pinion 54 extends only over the tangential region so that themass balls 18 are in contact with the pinion gearing 55 over an angle atcircumference of at most 45° and are then discharged in the openingformed rectilinearly relative to the channel 56. For said purpose, acollecting container 71 is formed in the housing 51, there beingassociated with the outlet of the channel 56 an open collecting tube 70made of an elastic material, by means of which the discharged mass balls18 are braked.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

We claim:
 1. A rotary tightening device for a safety belt, said rotarytightening device comprising:a belt retractor comprising a housing and abelt take-up shaft rotatably supported in said housing, saidbelt-take-up shaft having one end of the safety belt connected theretoand, upon triggering of said rotary tightening device, being rotated ina belt take-up direction of the safety belt; a drive wheel connected tosaid shaft; said housing having a channel extending in a plane parallelto a radial plane of said drive wheel and extending at least partiallyabout a circumference of said drive wheel; mass bodies unattached to oneanother and positioned loosely adjacent to one another in said channel;said mass bodies, when accelerated, acting on said drive wheel fordriving said drive wheel; said drive wheel having at the circumference agearing having recceses in which said mass bodies are form fittinglyreceived for driving said drive wheel, wherein a spacing betweenadjacent recesses of said gearing is substantially identical to aspacing between adjacent ones of said mass bodies.
 2. A rotarytightening device according to claim 1, wherein said gearing is designedsuch that said mass bodies, when received in said gearing, contact oneanother.
 3. A rotary tightening device according to claim 2, whereinsaid of recesses are projecting radially inwardly from the circumferenceof said drive wheel.
 4. A rotary tightening device according to claim 1,wherein said are cup-shaped and positioned recesses at the circumferenceof said drive wheel, said cup-shaped recesses having a shape matching ashape of said mass bodies.
 5. A rotary tightening device according toclaim 4, wherein said cup-shaped recesses are positioned along theentire circumference and are contiguous.
 6. A rotary tightening deviceaccording to claim 4, wherein said cup-shaped recesses are positionedalong the entire circumference and slightly overlap one another.
 7. Arotary tightening device according to claim 4, wherein said mass bodiesare balls and wherein said cup-shaped recesses are sphericalhalf-shells.
 8. A rotary tightening device according to claim 7, whereina radius of said cup-shaped recesses originates at a circle defined bythe theoretical points of contact of successive ones of said balls.
 9. Arotary tightening device according to claim 8, wherein each one of saidcup-shaped recesses widens radially outwardly in a funnel shape.
 10. Arotary tightening device according to claim 8, wherein said cup-shapedrecesses have transitions into neighboring ones of said cup-shapedrecesses.
 11. A rotary tightening device according to claim 10, whereinsaid transitions between said cup-shaped recesses are produced byrolling a milling cutter for milling said cup-shaped recesses along acircular path, having a radius identical to said radius of saidcup-shaped recesses.
 12. A rotary tightening device according to claim7, further comprising a casing for securing said balls therein.
 13. Arotary tightening device according to claim 12, wherein said casingcomprises a plastic tube in which said balls are positioned.
 14. Arotary tightening device according to claim 12, wherein said casing isan extrusion coating applied to said balls.
 15. A rotary tighteningdevice according to claim 7, further comprising a collecting chamber forsaid drive balls, wherein said balls are guided tangentially along thecircumference of said drive wheel for driving said drive wheel andthereafter are collected in said collecting chamber.
 16. A rotarytightening device according to claim 15, wherein an angular distance ofinteraction between said balls and said gearing is up to 45°.
 17. Arotary tightening device according to claim 7, wherein said drive wheelhas a peripheral groove cutting through said cup-shaped recesses andwherein said housing has sword-shaped guides for said mass balls, saidsword-shaped guides extending into said groove.
 18. A rotary tighteningdevice according to claimed 17, wherein said drive wheel has an inletregion for said balls and an outlet region for said balls, wherein oneof said sword-shaped guides is positioned at said inlet region andanother of said sword-shaped guides is positioned at said outlet region.19. A rotary tightening device according to claim 17, wherein said drivewheel is divided into two halves in the area of said groove and one ofsaid halves is connected to said belt take-up shaft.
 20. A rotarytightening device according to claim 19, wherein said half connected tosaid belt take-up shaft and said belt take-up shaft are a unitary part.21. A rotary tightening device according to claim 19, wherein a firstone of said halves consists of a different material than a second one ofsaid halves.
 22. A rotary tightening device according to claim 1, hereinan outside diameter of said drive wheel is greater than a thrustdiameter of said drive wheel by a distance≦a diameter of said massbodies.
 23. A rotary tightening device according to claim 1, furthercomprising a collecting device for collecting said mass bodies when saidmass bodies are exiting from said drive wheel, said collecting devicecomprising an open, flexible collecting tube and a collecting chamber,said collecting tube opening into said collecting chamber.
 24. A rotarytightening device according to claim 1, further comprising a collectingdevice for collecting said mass bodies when said mass bodies are exitingfrom said drive wheel, said collecting device comprising a foldedreceptacle positioned within a contour of said rotary tightening device,wherein said receptacle is structured to unfold upon triggering of saidrotary tightening device.
 25. A rotary tightening device for a safetybelt, said rotary tightening device comprising:a belt retractorcomprising a housing and a belt take-up shaft rotatably supported insaid housing, said belt-take-up shaft having one end of the safety beltconnected thereto and, upon triggering of said rotary tightening device,being rotated in a belt take-up direction of the safety belt; a drivewheel connected to said shaft; said housing having a channel extendingin a plane parallel to a radial plane of said drive wheel and extendingat least partially about a circumference of said drive wheel; massbodies unattached to one another and positioned loosely adjacent to oneanother in said channel; said drive wheel positioned such that said massbodies, when accelerated, act on said drive wheel for driving said drivewheel; said channel being a tube connected to said belt retractor; saidtube bent so as to provide a helical course for said mass bodiesextending from the outside inwardly toward said shaft and having adecreasing radius along said helical course in a direction toward saidshaft.
 26. A rotary tightening device according to claim 25, furthercomprising a cap made of resistant material for mounting said tube tosaid retractor, wherein said cap has a receiving element forpositive-lockingly securing said tube at said cap.
 27. A rotarytightening device according to claim 26, wherein said tube has a beadand wherein said cap has a matching throat for receiving said bead. 28.A rotary tightening device according to claim 26, wherein said tube hasa free end with a U-shaped suspending member and wherein said cap has amatching receiver for receiving said U-shaped suspending member.
 29. Arotary tightening device according to claim 25, wherein said tube ismounted in a load-transmitting manner on said housing of said beltretractor.
 30. A rotary tightening device according to claimed 25,further comprising a cap, consisting of plastic material, connected tosaid housing of said belt retractor, wherein said tube is embedded insaid cap.
 31. A rotary tightening device according to claim 25, whereinsaid tube is seamless.
 32. A rotary tightening device according to claim25, wherein said tube is comprised of tube halves seam-welded to oneanother.
 33. A rotary tightening device according to claim 25, furthercomprising a gas generator mounted within said tube, said gas generatoraccelerating sequentially said mass bodies, when activated, in alongitudinal direction of said gas generator, said tube having securingelements for positive-lockingly securing said gas generator.
 34. Arotary tightening device according to claim 33, further comprising adrive piston consisting of elastic material and positioned between saidgas generator and said mass bodies.
 35. A rotary tightening deviceaccording to claim 34, wherein said drive piston is secured in said tubeat a distance to said gas generator for defining an initial volume, saidtube having means for positive-lockingly securing said drive piston. 36.A rotary tightening device according to claim 35, further comprising apressure relief device positioned in an area between said drive pistonand said gas generator where said initial volume is defined, saidpressure relief device comprising a breaking point forming a window forpressure relief when a pressure threshold is surpassed.
 37. A rotarytightening device according to claim 34, further comprising a springpositioned between said drive piston and said gas generator forsupporting said piston.
 38. A rotary tightening device according toclaim 34, wherein said drive piston has a periphery with an elastic,outwardly directed spreading means and wherein said tube has a groovepositioned in a running direction of said mass bodies at a free end ofsaid tube, wherein said spreading means engages said groove after allmass bodies have been released from said tube.
 39. A rotary tighteningdevice according to claim 33, wherein said tube has an end comprisingbores from which end said mass bodies are discharged, said boresallowing escape of the propellant of said gas generator.
 40. A rotarytightening device according to claim 25, further comprising a collectingdevice for collecting said mass bodies when said mass bodies are exitingfrom said drive wheel, said collecting device comprising an open,flexible collecting tube and a collecting chamber, said collecting tubeopening into said collecting chamber.
 41. A rotary tightening deviceaccording to claim 25, further comprising a collecting device forcollecting said mass bodies when said mass bodies are exiting from saiddrive wheel, said collecting device comprising a folded receptaclepositioned within a contour of said rotary tightening device, whereinsaid receptacle is structured to unfold upon triggering of said rotarytightening device.